This invention relates to a method and apparatus for removing particulate matter from the intake air of a chain saw internal combustion engine.
In the past portable chain saws have been extensively utilized. These devices generally comprise an internal combustion engine, a guide bar and an endless cutting chain carried by the guide bar and operatively connected to a crankshaft of the internal combustion engine. In order to facilitate portabiliy of these units the internal combustion engines are generally of the small one or two cylinder, two cycle, air cooled type.
The working environment for portable chain saws may range from logging camps to a homeowner's backyard. Almost universally, however, where portable chain saws possess a degree of utility, a common environmental denominator is the notable presence of dust, dirt and debris which is kicked up during a cutting operation. In this connection, air suspended debris or temporary atmospheric impurities may range from coarse matter such as relatively large sticks and leaves to very fine dust particles which may be as small as one micron in diameter. Since air suspended debris surrounds the operating saw it is highly subject to being sucked into the carburetor and the operating cycle of the internal combustion engine. Such foreign matter has long been known to possess deleterious effects both in terms of clogging accurately dimensioned carburetor and valve passages and also producing considerable abrasion wear within the interior of the combustion cylinders. Therefore, it would be highly desirable to eliminate or minimize the amount of particulate material that is drawn into the combustion cycle of a chain saw internal combustion engine along with the intake air.
In the past it has been common practice in the chain saw industry merely to utilize a conventional diaphragm or canister type filer for removing entrained matter from the inlet air. While such filters have exhibited a wide degree of utility room for improvement remains. More particularly previously known filter units by necessity have been produced with a considerable design compromise. On the one hand, if a coarse tortuous path filter is specified, fine particles easily pass through the filter and the engine is quickly damaged. If, however, a fine filter is specified large particles quickly clog the unit requiring frequent cleaning and/or replacement in order to maintain enough air flow into the carburetor to meet minium air/fuel mixture requirements. Moreover, if the chain saw is utilized in relatively cool climatic regions, moisture, held within a dust laden filter may freeze and block off air flow through the unit.
A refinement over the mere provision of a conventional inlet flter is disclosed in a U.S. Mansfield Pat. No. 2,825,318, issued Mar. 4, 1958. The Mansfield patent discloses an apparatus for supplying air to the carburetor of an internal combustion engine which utilizes, in combination with an intake screen, a rotary fan of the centrifugal type. The fan serves to impel air and entrained matter radially away from a crankshaft and out through a surrounding shroud. Intake air to the carburetor is drawn from within the shroud at a position behind a baffle positioned to separate the fan from an aperture in the shroud. By the provision of the above structure, a conventional air filter has been eliminated while dirt and dust within the inlet air is, at least to a degree, separated out of the air ultimately fed into the internal combustion engine. While the Mansfield apparatus is at least theoretically appealing room for significant improvement remains.
In this connection it will be noted that to the extent fine particulate matter remains entrained within the air that is drawn behind the baffle it will be directly pulled into the carburetor and the combustion cycle. Therefore, in many field applications where a large amount of fine dust and particulate matter is likely to be encountered it would be highly desirable to provide a method and apparatus for increasing the amount of foreign material that may be removed from the inlet air prior to the air entering the combustion system.